Catheters are widely used in medical applications. They have been particularly useful in treating an enlarged prostate by microwave treatment. For this application, a catheter is inserted into the urethra of the man to be treated until an inflatable balloon, which is located at the front insertion end of the catheter, is positioned in the urinary bladder. The balloon is then inflated and held stationary within the bladder. Subsequently, a microwave antenna is inserted through an inner lumen of the catheter until it is located adjacent to the prostate. The antenna is arranged at the front end of an antenna cable, while the other end of the cable, which protrudes from the catheter, is connected with a microwave energy source.
In the vicinity of the bladder the urethra has a relatively sharp bend. The catheter must be highly flexible and easily bendable.
Since the microwave antenna is located within the catheter, the microwave energy must be radiated through the catheter wall to the prostate. Not all materials are suitable for construction of the catheter.
A conventional catheter for the microwave treatment of the prostate uses a multi-lumen catheter tube made of polyvinylchloride (PVC). Such a PVC catheter is highly flexible but not satisfactory from an electrical point of view. PVC excessively attenuates microwaves and therefore heats up. As a consequence, the catheter tube softens and the surrounding body tissue is subjected to undesirable heat.
DE2728636 C2 describes a small tube for medical endoscopes, in particular gastroscopes, with a 3-layer construction comprising an impermeable intermediate layer, an outer layer and an inner layer. The outer layer and the inner layer consist of a porous polymerisate with fibril structure, for instance porous polytetrafluoroethylene (PTFE). The intermediate layer may consist of a flexible metal film or a thin flexible plastic material such as fluorinated ethylene propylene (FEP), copolymer, perfluoroalkoxy resin (PFA) or polyvinylchloride (PVC). A flexible metal film makes this small existing tube unsuitable for any use as a catheter for inserting an antenna which radiates microwave energy. The metal film completely shields off the microwave energy. The proposed use of plastic materials, such as PVC, for the small known tube, is unsuitable because it has too strong an attenuation for the microwave energy, (i.e. absorbs too much microwave energy).
There is a need to provide a flexible catheter that is easily bendable but maintains desirable electrical and attenuation properties.